Portable electrostatic spray devices useful for spraying liquid compositions, and particularly those which utilize a removable cartridge, are known in patent publications such as WO 01/12336, WO 01/12335, US 2001-0020653A, US 2001-0038047A, US 2001-0020652A, and US 2001-0023902A. As recognized in the art, the design of an electrostatic spray device starts with identifying spray quality factors such as spray droplet diameter, distribution of spray droplet diameter, and spray area at the target distance from the object to be sprayed. To achieve the target spray quality, the output operating variables of the device such as: high voltage output, current output, product flow rate; are balanced with the properties of the liquid composition such as: viscosity, resistivity, surface tension. For a given set of environmental factors; such as temperature and humidity; combined with the device operating variables and liquid composition properties, a particular charge-to-mass ratio exists for a specific target spray quality. The charge-to-mass ratio is a measure of the amount of electrical charge carried by the atomized spray on a per weight basis and may be expressed in terms of coulombs per kilogram (C/kg). The charge-to-mass ratio provides a useful measure to ensure that good spray quality is maintained. A change during spraying in any of the liquid composition properties or device output operating variables will result in a change in the spray quality.
An important factor for providing constant liquid composition properties relates to stability of the liquid composition to be sprayed. Maintaining stability of the liquid composition is particularly important for liquid compositions that are emulsions, thereby having conductive and insulating phases, as high electric field gradients from within the reservoir can cause electrical current to flow through the liquid composition and cause the liquid composition to separate into its conductive and insulating phases. Further, the electrically induced separation of the liquid composition can change one or more of the liquid composition properties, for example, viscosity, resistivity, surface tension, and therefore can change the charge-to-mass ratio of the resulting spray. Separation of the liquid composition per se is disadvantageous for the user, as it may alter the functional performance expected by the liquid composition.
The art provides methods for providing the target charge-to-mass ratio in a consistent manner by, for example, reducing the electric field gradients and in turn preventing electrical current from flowing through the reservoir by incorporating a high voltage shield to stabilize the area surrounding the reservoir and to prevent current leakage from the reservoir to adjacent locations within the device at lower electrical potentials. Another method suggested is to limit the volume of the liquid composition located between the electrode charging location and nozzle, thereby minimizing the volume of liquid composition that has been electrically induced separation. Specifically suggested is a straight narrow nozzle pathway between the electrode charging location and nozzle.
While these methods are successful in providing electrostatic spray devices that are safe upon use and provide good spray quality, it is difficult and/or uneconomical to manufacture the nozzle pathway and its vicinity for mass production, due to difficulty of providing a straight, yet precise small diameter nozzle pathway.
Based on the foregoing, there is a need for a portable electrostatic spray device and/or a removable cartridge for the portable electrostatic spray device; which provides good spray quality while being safe for the user, and which is manufactured in a convenient, economical manner. There is further a need for a portable electrostatic spray device, for spraying an emulsion liquid composition, which can maintain the emulsion liquid composition while spraying. There is further a need for a portable electrostatic spray device, for spraying an emulsion liquid composition, which provide various usage advantages to the user.
None of the existing art provides all of the advantages and benefits of the present invention.